Service Manual

ForwardDirection(continued)
Whengoingdownahill,thetractorbecomesanover−runningloadthatdrives
thefrontwheelandrearaxlemotors.Inthiscondition,therearaxlemotorcould
lockupastheoilpumpedfromthemotorincreasespressureasitreturnstothe
pistonpump.Topreventrearwheellockup,anadjustablereliefvalve(RV)in
thereartractionmanifoldreducesrearaxlemotorpressurecreatedindownhill,
dynamicbrakingconditions.
ReverseDirection
ThetractioncircuitoperatesessentiallythesameinreverseHIspeed(transport)
asitdoesintheforwarddirection.However,theowthroughthecircuitis
reversed.Oilowfromthepistonpumpisdirectedtothefrontwheelmotorsand
alsotothereartractionmanifold.Theoiltothefrontwheelmotorsdrivesthem
inthereversedirectionandthenreturnstothepistonpumpthroughthefront
tractionmanifold.Theoiltothereartractionmanifoldentersthereartraction
manifoldatportP2andowsthroughpressurereducingvalve(PR)whichlimits
thedownstreampressuretotherearaxlemotorto26bar(380PSI)sotherear
wheelswillnotscufftheturfduringreverseoperation.Thisreducedpressure
owisdirectedoutreartractionmanifoldportM8todrivetherearaxlemotorin
reverse.Returnoilfromtherearmotorreturnstothepistonpumpthroughthe
fronttractionmanifold.
Groundsmaster
®
4000-D&4010-D
Page5–19
HydraulicSystem:HydraulicFlowDiagrams
13202SLRevF